Mandrel with differential in thermal expansion to eliminate wrinkles in ply

ABSTRACT

An aircraft stringer lay-up assembly is provided comprising a first mandrel element having a first mandrel material with a first mandrel coefficient of thermal expansion. A composite ply assembly is laid up onto the first mandrel element to generate a primary lay-up surface. The composite ply assembly comprises a first primary fold-over portion folded onto to the first mandrel right end surface. A second primary fold over portion folds over to the first mandrel left end surface. The first mandrel coefficient of thermal expansion is adapted such that the first mandrel is movable between a first mandrel normal condition and a first mandrel heated condition where the first mandrel right end surface and the first mandrel left end surface move away from each other. The first primary fold-over portion and the secondary primary fold over portion are thereby moved such that wrinkles are pulled out of said primary lay-up surface.

TECHNICAL FIELD

The present invention relates generally to an aircraft stringer lay-up assembly and more particularly to an apparatus and method for reducing the presence of wrinkles in a primary lay-up surface of a composite aircraft stringer.

BACKGROUND OF THE INVENTION

Aircraft components such as stringers have become complex in design and shape due to developing aircraft designs. The complexity of shape in combination with a need for decreased weight/strength ratios requires the use of alternate construction technologies. For this reason, aircraft designers have turned to the use of composite ply assemblies for the manufacture of aircraft stringers. In these manufacturing scenarios, a material ply impregnated with epoxy or similar substance is layed-up onto a mandrel shaped to generated the complex shape. The composite ply assembly is then cured to generate a composite component with the desired complex shape.

The nature of laying up material plies onto complex shaped mandrels, however, generates a plurality of manufacturing concerns and issues. One of such issues is the generation of wrinkles in the lay-up surfaces of the final component. These wrinkles can interfere with final assembly and may even in some circumstances weaken the strength of the final component. This is clearly undesirable. In addition, the complex shaping of the mandrels often places limits on the mandrel construction techniques. Standard metal fabrication of mandrels often is overly costly and cannot reliably result in the precise complex structures required for modern aircraft design requirements. The use of composite mandrel assemblies partially alleviates these concerns, but in turn results in costly mandrels that are easily damaged and do not have the lifespan of the metal fabricated counterparts.

It would, therefore, be highly desirable to have an aircraft stringer lay-up assembly with improved removal of wrinkles from the lay-up surfaces. It would additionally be highly desirable to have such an apparatus and method that was compatible with inexpensive and increased lifespan mandrels.

SUMMARY OF THE INVENTION

It is therefore an object to the present invention to provide an aircraft stringer lay-up assembly with improved wrinkle removal characteristics. It is further object of the present invention to provide an apparatus and method for the removal of wrinkles in aircraft stringer lay-up assemblies with improvements to cost and lifespan.

In accordance with the objects of the present invention an aircraft stringer lay-up assembly is provided comprising a first mandrel element having a first mandrel material with a first mandrel coefficient of thermal expansion. A composite ply assembly is laid up onto the first mandrel element to generate a primary lay-up surface. The composite ply assembly comprises a first primary fold-over portion folded onto to the first mandrel right end surface. A second primary fold over portion folds over to the first mandrel left end surface. The first mandrel coefficient of thermal expansion is adapted such that the first mandrel is movable between a first mandrel normal condition and a first mandrel heated condition where the first mandrel right end surface and the first mandrel left end surface move away from each other. The first primary fold-over portion and the secondary primary fold over portion are thereby moved such that wrinkles are pulled out of said primary lay-up surface.

Other objects and features of the present invention will become apparent when viewed in light of the detailed description and preferred embodiment when taken in conjunction with the attached drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an aircraft stringer lay-up assembly in accordance with the present invention.

FIG. 2 is a detailed illustration of the aircraft stringer lay-up assembly illustrated in FIG. 1, the assembly illustrated subjected to a first mandrel heated condition.

FIG. 3 is an illustration of the aircraft stringer lay-up assembly illustrated in FIG. 1, the assembly illustrated including a vacuum bag assembly.

FIG. 4 is a detailed illustration of the aircraft stringer lay-up assembly illustrated in FIG. 1, the assembly illustrated including a clamping assembly.

FIG. 5 is a detailed illustration of the aircraft stringer lay-up assembly illustrated in FIG. 1, the assembly illustrated including a heating element positioned within the first mandrel element.

FIG. 6 is a detailed illustration of the aircraft stringer lay-up assembly illustrated in FIG. 1, the assembly illustrated including a perpendicular excess portion.

FIG. 7 is an illustration of a resultant contoured I-beam element as a result of the aircraft stringer lay-up assembly illustrated in FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to FIG. 1, which is an illustration of an aircraft stringer lay-up element 10 in accordance with the present invention. The aircraft stringer lay-up element 10 includes a first mandrel element 12, preferably an elongated metal beam element 14 as shown. The present invention can further include a second mandrel element 16. The fist mandrel element 12 can include a plurality of rigidity reducing first slots 18, preferably produced through wire electrical discharge machining, formed over a first mandrel length 20 and protruding partially through a first mandrel depth 22 as described in the co-pending application herein incorporated by reference. The mandrels 12,16 are thereby free to conform to a contoured curing block 24 on which they may be laid.

The first mandrel element 12 is comprised of a first mandrel vertical upper surface 26, a first mandrel vertical lower surface 28, two first mandrel side surfaces 30, a first mandrel right end surface 32 located at a first mandrel right end 34 and a first mandrel left end surface 36 located at a first mandrel left end 38. A composite ply assembly 40 is laid-up onto said first mandrel element 12 to generate a primary lay-up surface 42. Although a variety of primary lay-up surfaces 42 are contemplated, one embodiment contemplates the primary lay-up surface 42 to be coincident with the first mandrel vertical upper surface 26. The composite ply assembly 40 further includes a first primary excess portion 44 (also referred to as a fold-over portion) and a second primary fold over portion 46. The first primary excess portion 44 is affixed to the first mandrel right end 34. In the case of using fold over embodiment, the first primary fold-over portion 44 is folded over to engage the first mandrel right end surface. Similarly the second primary excess portion 46 is affixed to the first mandrel left end 38 by folding over the second primary fold-over portion 46 onto the first mandrel left end surface 36.

The present invention contemplates that the fist mandrel element 12 is comprised of a first mandrel material 48 having a first mandrel coefficient of thermal expansion (COE) 50. The composite ply assembly 40 is preferably comprised of a composite COE 52 significantly less than the first mandrel COE 50. This allows the first mandrel 12 to be moved between a first mandrel normal condition 54 (FIG. 1) and a first mandrel heated condition 56 (FIG. 2). The first mandrel heated condition 56, as a result of the first mandrel COE 50 causes the first mandrel right end surface 32 to move away from the first mandrel left end surface 34 such that the primary lay-up surface 42 of the composite ply assembly 40 is pulled taught and any wrinkles during lay-up are removed.

The heat required to move the first mandrel element 12 from the first mandrel normal condition 54 to the first mandrel heated condition 56 may be introduced in a variety of fashions. In one embodiment, the heat is provided through the curing heat 58 used to cure the composite ply assembly 40. In other embodiments, however, such as the example shown in FIG. 5, the heat may be provided independent of curing such as through the use of a heating element 60 positioned within the first mandrel element 12. This allows the present invention to be implemented in lay-up configurations wherein the composite ply assembly 40 is cured without heat. In still another considered embodiment, the heating element 60 (FIG. 5) can be used as a source of heat for controlling size of the first mandrel element 12 in addition to being a source of the curing heat 58 used to cure the composite ply assembly 40.

The present invention may be further improved by including a secondary lay-up surface 62 coincident with the first mandrel vertical lower surface 32. The composite ply assembly 40 thereby includes a first secondary excess (fold-over) portion 64 and a second secondary excess (fold-over) portion 66 affixed/folded over the first mandrel right end surface 32 and fist mandrel left end surface 36 respectively. The secondary excess portions 64,66 engage the primary excess portions 44,46 such that a stronger stretching force can be induced in the primary lay up surface 42 and the secondary lay-up surface 62. Although using fold-over technology may be utilized to secure excess portions, the present invention may further utilize a clamping assembly 68 (see FIG. 4) or a vacuum bag assembly 70 (FIGS. 3 and 5) as means to adequately secure that composite ply assembly 40 to the first mandrel element 12 such that expansion of the mandrel element 12 due to its first mandrel COE 50 can be harnessed to remove wrinkles.

The second mandrel element 16 should similarly have a second mandrel coefficient of thermal expansion 72 which preferably matches said first mandrel COE 50. The second mandrel element 16 is preferably placed adjacent the first mandrel element 12 such that the composite ply assembly 40 may be laid up between the two mandrels 12,16 in addition to over the first mandrel upper vertical surface 26 and a second mandrel upper vertical surface 74, and over a first mandrel lower vertical surface 28 and a second mandrel lower vertical surface 76. In this fashion, a contoured I-beam element 78 is formed. The fold-over portions 44,46,64,66 (or excess portions) can be removed (trimmed) after curing such that a pristine contoured I-beam element 78 is produced (see FIG. 7).

In still another embodiment, the composite ply assembly 40 may further include a first perpendicular fold-over portion 80 and a second perpendicular fold-over portion 82 perpendicular to the primary fold over portions 44,46. These perpendicular fold over portions 80,82 are folded over or affixed to the first mandrel side surfaces 30 opposing each other. This results in the primary lay-up surface 42 being stretched in a first planar direction 84 and a second planar direction 86 such that addition wrinkle removal is provided.

While the invention has been described in connection with one or more embodiments, it is to be understood that the specific mechanisms and techniques which have been described are merely illustrative of the principles of the invention, numerous modifications may be made to the methods and apparatus described without departing from the spirit and scope of the invention as defined by the appended claims. 

1. An aircraft stringer lay-up assembly comprising: a first mandrel element comprised of a first mandrel material having a first mandrel coefficient of thermal expansion, said first mandrel element having a first mandrel vertical upper surface, a fist mandrel vertical lower surface, two first mandrel side surfaces, a first mandrel right end surface and a first mandrel left end surface; and a composite ply assembly laid up onto said first mandrel element to generate a primary lay-up surface, said composite ply assembly comprising: a first primary fold-over portion extending from said primary lay-up surface and folding to said first mandrel right end surface; and a second primary fold over portion extending from said primary lay-up surface and folding over to said first mandrel left end surface; wherein said first mandrel coefficient of thermal expansion is adapted such that said first mandrel is movable between a first mandrel normal condition and a first mandrel heated condition, said first mandrel right end surface and said first mandrel left end surface move away from each other when in said first mandrel heated condition, said first primary fold-over portion and said secondary primary fold over portion moved by said first mandrel right end surface and said first mandrel left end surface when in said first mandrel heated condition such that wrinkles are pulled out of said primary lay-up surface.
 2. An aircraft stringer lay-up assembly as described in claim 1, wherein said first mandrel element comprises: an elongated beam.
 3. An aircraft stringer lay-up assembly as described in claim 1, wherein said composite ply assembly further comprises: a secondary lay-up surface laid up on said first mandrel element opposite said primary lay-up surface; a first secondary fold-over portion extending from said secondary lay-up surface and folding to said first mandrel right end surface; and a second secondary fold over portion extending from said secondary lay-up surface and folding over to said first mandrel left end surface.
 4. An aircraft stringer lay-up assembly as described in claim 3, wherein said first secondary fold-over portion engages said first primary fold-over portion, said second secondary fold-over portion engaging said second primary fold-over portion.
 5. An aircraft stringer lay-up assembly as described in claim 1, further comprising: a heating element positioned within said first mandrel element.
 6. An aircraft stringer lay-up assembly as described in claim 3, wherein said primary lay-up surface is positioned on a first mandrel side surface and said secondary lay up-surface is positioned on an opposing first mandrel side surface.
 7. An aircraft stringer lay-up assembly as described in claim 1, wherein said first coefficient of thermal expansion is adapted such that a curing temperature of said composite ply assembly moves said first mandrel element into said first mandrel heated condition.
 8. An aircraft stringer lay-up assembly as described in claim 1, wherein said first coefficient of thermal expansion is significantly greater than a composite coefficient of thermal expansion of said composite ply assembly.
 9. An aircraft stringer lay-up assembly as described in claim 1, further comprising: at least on clamping assembly affixing said first primary fold over portion to said first mandrel right end surface.
 10. An aircraft stringer lay-up assembly as described in claim 1, further comprising: a vacuum bag assembly surrounding said first mandrel element and said composite ply assembly, said vacuum bag assembly pressing said composite ply assembly against said first mandrel element during curing.
 11. An aircraft stringer lay-up assembly as described in claim 1, further comprising: a contoured curing block; and a plurality of rigidity reducing first slots formed along a first mandrel length of said first mandrel element, said plurality of rigidity reducing first slots protruding partially through a first mandrel depth of said first mandrel element to allow said first mandrel element to conform to said contoured curing block.
 12. An aircraft stringer lay-up assembly as described in claim 11, wherein each of said plurality of rigidity reducing first slots comprises a wire electrical discharged machined slot.
 13. An aircraft stringer lay-up assembly as described in claim 1, further comprising: a second mandrel element positioned adjacent said first mandrel element, said second mandrel having a second mandrel coefficient of thermal expansion equal to said first mandrel coefficient of thermal expansion.
 14. An aircraft stringer lay-up assembly as described in claim 13, wherein said composite ply assembly is laid up between said first mandrel element and said second mandrel element, said composite ply assembly extending over a first mandrel upper vertical surface and a second mandrel upper vertical surface, said composite ply assembly extending over a first mandrel lower vertical surface and a second mandrel lower vertical surface such that said composite ply assembly comprises a contoured I-beam element.
 15. An aircraft stringer lay-up assembly as described in claim 1, wherein said composite ply assembly further comprises: a first perpendicular fold-over portion extending from said primary lay-up surface and folding to one of said first mandrel side surfaces; and a second perpendicular fold-over portion extending from said primary lay-up surface and folding to another of said first mandrel side surfaces; wherein first perpendicular fold over portion is perpendicular to said first primary fold over portion such that said primary lay-up surface is stretched in two planar directions as said first mandrel element is moved into said first mandrel heated condition.
 16. An aircraft stringer lay-up assembly comprising: a first mandrel element comprised of a first mandrel material having a first mandrel coefficient of thermal expansion, said first mandrel element having a first mandrel vertical upper surface, a fist mandrel vertical lower surface, two first mandrel side surfaces, a first mandrel right end and a first mandrel left end; and a composite ply assembly having a composite ply coefficient of thermal expansion, said composite ply assembly laid up onto said first mandrel element to generate a primary lay-up surface, said composite ply assembly comprising: a first primary excess portion extending from said primary lay-up surface and affixed to said first mandrel right end; and a second primary excess portion extending from said primary lay-up surface and affixed to said first mandrel left end; wherein said first mandrel coefficient of thermal expansion is substantially larger than said composite ply coefficient of thermal expansion such that said first mandrel is movable between a first mandrel normal condition and a first mandrel heated condition, said first mandrel right end and said first mandrel left end move away from each other when in said first mandrel heated condition, said first primary excess portion and said secondary primary excess portion thereby pulled apart in said first mandrel heated condition such that wrinkles are pulled out of said primary lay-up surface.
 17. An aircraft stringer lay-up assembly as described in claim 16, wherein said first mandrel element comprises: an elongated beam.
 18. An aircraft stringer lay-up assembly as described in claim 16, wherein said composite ply assembly further comprises: a secondary lay-up surface laid up on said first mandrel element opposite said primary lay-up surface; a first secondary excess portion extending from said secondary lay-up surface and affixed to said first mandrel right end; and a second secondary excess portion extending from said secondary lay-up surface and affixed to said first mandrel left end.
 19. An aircraft stringer lay-up assembly as described in claim 18, wherein said first secondary excess portion engages said first primary excess portion, said second secondary excess portion engaging said second primary excess portion.
 20. An aircraft stringer lay-up assembly as described in claim 16, wherein said first coefficient of thermal expansion is adapted such that a curing temperature of said composite ply assembly moves said first mandrel element into said first mandrel heated condition.
 21. An aircraft stringer lay-up assembly as described in claim 16, further comprising: at least on clamping assembly affixing said first primary excess portion to said first mandrel right end.
 22. An aircraft stringer lay-up assembly as described in claim 16, further comprising: a vacuum bag assembly surrounding said first mandrel element and said composite ply assembly, said vacuum bag assembly affixing said first primary excess portion to said first mandrel right end during curing.
 23. An aircraft stringer lay-up assembly as described in claim 16, further comprising: a contoured curing block; and a plurality of rigidity reducing first slots formed along a first mandrel length of said first mandrel element, said plurality of rigidity reducing first slots protruding partially through a first mandrel depth of said first mandrel element to allow said first mandrel element to conform to said contoured curing block, each of said plurality of rigidity reducing first slots comprising a wire electrical discharged machined slot.
 24. An aircraft stringer lay-up assembly as described in claim 16, further comprising: a second mandrel element positioned adjacent said first mandrel element, said second mandrel having a second mandrel coefficient of thermal expansion equal to said first mandrel coefficient of thermal expansion.
 25. An aircraft stringer lay-up assembly as described in claim 24, wherein said composite ply assembly is laid up between said first mandrel element and said second mandrel element, said composite ply assembly extending over a first mandrel upper vertical surface and a second mandrel upper vertical surface, said composite ply assembly extending over a first mandrel lower vertical surface and a second mandrel lower vertical surface such that said composite ply assembly comprises a contoured I-beam element.
 26. An aircraft stringer lay-up assembly as described in claim 16, wherein said composite ply assembly further comprises: a first perpendicular excess portion extending from said primary lay-up surface and affixed to one of said first mandrel side surfaces; and a second perpendicular excess portion extending from said primary lay-up surface and affixed to another of said first mandrel side surfaces; wherein first perpendicular excess portion is perpendicular to said first primary excess portion such that said primary lay-up surface is stretched in two planar directions as said first mandrel element is moved into said first mandrel heated condition.
 27. A method of laying up an aircraft stringer comprising: manufacturing a first mandrel element from a first mandrel material having a first mandrel coefficient of thermal expansion, said first mandrel element having a first mandrel vertical upper surface, a fist mandrel vertical lower surface, two first mandrel side surfaces, a first mandrel right end surface and a first mandrel left end surface; laying up a composite ply assembly onto said first mandrel element to generate a primary lay-up surface, said composite ply assembly comprising a first primary fold-over portion and a second primary fold over portion extending from said primary lay-up surface; folding over said first primary fold-over portion onto said fist mandrel right end surface; folding over said second primary fold-over portion onto said first mandrel left end surface; heating said first mandrel element such that said first mandrel moves between a first mandrel normal condition to a first mandrel heated condition, said first mandrel coefficient of thermal expansion moving said first mandrel right end surface away from said first mandrel left end surface as said mandrel enters said first mandrel heated condition, said first primary fold-over portion moving away from said secondary primary fold-over portion in response to relative movement of said first mandrel right end surface and said first mandrel left end surface such that wrinkles are pulled out of said primary lay-up surface; and curing said composite ply assembly to form a composite stringer element.
 28. A method as described in claim 27, wherein said first coefficient of thermal expansion is significantly greater than a composite coefficient of thermal expansion of said composite ply assembly.
 29. A method as described in claim 27, further comprising: laying up said composite ply assembly onto a secondary lay-up surface on said first mandrel element; folding over a first secondary fold-over portion onto said first mandrel right end surface; folding over a second secondary fold-over portion onto said first mandrel left end surface.
 30. A method as described in claim 29, further comprising: engaging said first primary fold-over portion with said first secondary fold-over portion; and engaging said second primary fold-over portion with said second secondary fold-over portion.
 31. A method as described in claim 27, further comprising: clamping said first primary fold-over portion to said first mandrel right end surface.
 32. A method as described in claim 27 further comprising: placing said first mandrel element and said composite ply assembly into a vacuum bag assembly; and sealing said vacuum bag assembly such that said composite ply assembly is pressed against said first mandrel element during curing.
 33. A method as described in claim 27 further comprising: heating said first mandrel element by curing said composite ply assembly.
 34. A method as described in claim 27, further comprising: heating said first mandrel element through the use of a heating element positioned within said first mandrel element.
 35. A method as described in claim 27 further comprising: forming a plurality of rigidity reducing first elements in said first mandrel element along a first mandrel length; placing said first mandrel element on a contoured curing block, said plurality or rigidity reducing first elements allowing said first mandrel element to conform to said contoured curing block.
 36. A method as described in claim 35 wherein said plurality of rigidity reducing first element are formed using wire electrical discharge machining.
 37. A method as described in claim 27 further comprising: placing a second mandrel element adjacent said first mandrel element; laying up said composite ply assembly between said first mandrel element and said second mandrel element such that said composite ply assembly extends over a first mandrel upper vertical surface, a second mandrel upper vertical surface, a first mandrel lower vertical surface, and a second mandrel lower vertical surface such that said composite ply assembly comprises a contoured I-beam element.
 38. A method as described in claim 37 further comprising: trimming off said first primary fold-over portion and said second primary fold-over portion after curing said composite ply assembly.
 39. A method as described in claim 38, further comprising: folding a first perpendicular fold-over portion of said composite ply assembly from said primary lay-up surface to one of said fist mandrel side surfaces; folding a second perpendicular fold-over portion of said composite ply assembly from said primary lay-up surface to another of said first mandrel side surfaces; heating said first mandrel element such that said primary lay-up surface is stretched in two planar directions.
 40. A method of laying up an aircraft stringer comprising: manufacturing a first mandrel element from a first mandrel material having a first mandrel coefficient of thermal expansion, said first mandrel element having a first mandrel vertical upper surface, a fist mandrel vertical lower surface, two first mandrel side surfaces, a first mandrel right end surface and a first mandrel left end surface; laying up a composite ply assembly onto said first mandrel element to generate a primary lay-up surface, said composite ply assembly comprising a first primary excess portion and a second primary excess portion extending from said primary lay-up surface; attaching said first primary excess portion onto said fist mandrel right end; attaching over said second primary excess portion onto said first mandrel left end; heating said first mandrel element such that said first mandrel moves between a first mandrel normal condition to a first mandrel heated condition, said first mandrel coefficient of thermal expansion moving said first mandrel right end away from said first mandrel left end as said mandrel enters said first mandrel heated condition, said first primary excess portion moving away from said secondary primary excess portion in response to relative movement of said first mandrel right end and said first mandrel left end such that wrinkles are pulled out of said primary lay-up surface; and curing said composite ply assembly to form a composite stringer element.
 41. A method as described in claim 40, further comprising: forming a plurality of rigidity reducing first elements in said first mandrel element along a first mandrel length; placing said first mandrel element on a contoured curing block, said plurality or rigidity reducing first elements allowing said first mandrel element to conform to said contoured curing block.
 42. A method as described in claim 40, further comprising: clamping said first primary excess portion to said first mandrel right end.
 43. A method as described in claim 42 further comprising: clamping said first primary excess portion using a vacuum bag assembly. 